Assemblies and apparatus for winding a plurality of elongated elements such as wires, cables or cords on one spool are known in the art. However, the unwinding of a plurality of elongated elements from such a single spool, may cause difficulties and the subsequent twisting of the elongated elements, e.g. in a double-twisting machine, may lead to an unacceptable degree of fracture and process-ability problems.
The unwinding difficulties and the processability problems and fractures during the subsequent twisting may be due to a variation in diameter of the elongated elements during their winding, or may be due to the fact that elongated elements become entangled during their winding, or may be due to the fact that the elongated elements, although wound at the same time on the same spool, take different lengths on the spool. Other difficulties during the unwinding operations are due to different tensions in the individual elongated elements during the winding operation. According to Hooke's law, in case the tension on a first individual elongated element increases in comparison with the tension on a second individual elongated element, less material of the first individual elongated element will be wound since this first individual element gets more elongated.
In addition, tension measurement, particular tension measurement in-line, is expensive.
Prior art GB1163983B discloses a method for winding a plurality of elongated elements on one spool whereby it is aimed at keeping the winding lengths of the elongated elements substantially equal to each other despite some variations in diameter of the elongated element. The solution used to obtain substantially the same lengths is to increase the tension in elongated elements with an increased diameter in order to reduce the winding diameter and to decrease the tension in elongated elements with a decreased diameter in order to increase the winding diameter. A separation comb is mounted upstream the winding spool in order to avoid disentanglement of the neighboring elongated elements. But this prior art has its drawback. The tension difference between the elongated elements may cause unwinding difficulties during the unwinding process.
Prior art EP0780333A discloses an assembly for winding multiple elongated elements on a spool, where the tensions in the elongated elements are kept substantially constant and equal. In order to obtain constant and equal tensions, the assembly comprises following parts: a set of independently drivable capstans, one for each individual elongated element to be wound; a single spool where the plurality of elongated elements are to be wound; first monitoring means for measuring the tensions of each individual elongated element of a subgroup of the plurality of elongated elements; first control means for steering individually the revolution speed of the capstans driving the elongated elements of the subgroup such that said tensions remain substantially constant and substantially equal to each other. Before their winding on the spool, a comb is used to prevent the wires from entangling with each other and from jumping over each other. But this prior art also has its drawbacks. In this assembly, the tension of each elongated element is measured and controlled by an individual dancer arm. Because of the difference on manufacture, assembly, and calibration of the individual dancer arms, tension difference occurs between the elongated elements.